MULTISCALE VARIABILITY OF TROPICAL OCEAN ZOOPLANKTON BIOMASS

The variability of zooplankton biomass on a scale of thousands, hundre ds, and tens of kilometres was estimated from the data bank of over 40 expeditions to the Atlantic and Indian Oceans and seas of the Mediter ranean basin. Thirty oceanographic grid surveys were used to estimate variability on a scale of hundreds of kilometres. Continuous records w ithin these grids were used to estimate zooplankton variability on the scale of tens of kilometres, and high-resolution sampling was used to investigate variability of kilometre scale. In the multiscale variabi lity of zooplankton biomass, the maximum variability was observed on t he thousands of kilometres scale, with the quantitative values of biom ass represented in a form of normalized variance. The local peak of va riability of zooplankton biomass in the range of hundreds of kilometre s, in the tropical ocean, was probably due to the enhanced water dynam ics with the same scale range. This activity is linked with open-ocean mesoscale eddy fields in the tropical zones of both oceans. The other typical feature of the structure of the zooplanktonic fields is its s patial anisotropy, which indicates different properties of spatial var iation of parameters along directions through space. The anisotropy wa s evaluated by means of two-dimensional spatial autocorrelation functi ons. Two-dimensional correlation ellipses of the zooplankton biomass f ields were orientated by their main axes in accordance with the direct ion of transport of the main water mass, the direction of motion of th e eddies, and the orientation of divergence or convergence zones. The spatial heterogeneity of zooplankton biomass distribution in the horiz ontal plane can be characterized by the frequency of occurrence of pat ches. On a log scale the frequency of occurrence of different size pat ches diminishes proportionally with their linear size. Zooplankton bio mass is distributed more heterogeneously than that of phytoplankton (c hlorophyll a). Synchronous measurements of the three-level system ''ph ytoplankton-mesozooplankton-flying fish'' (where each component acts a s a prey item for the next one) exhibit the same trend of spatial auto correlation functions, diminishing over the trophic levels on a scale from hundreds to tens of kilometres. This means that relatively hetero geneous fields of predators exist on more uniformly distributed fields of their prey. (C) 1995 International Council for the Exploration of the Sea